1. Field of the Invention
The present invention relates to zoom lenses and image pickup apparatuses having the zoom lenses. The zoom lenses are suitably used in, for example, video cameras, electronic still cameras, broadcast cameras, silver-halide film cameras, and the like.
2. Description of the Related Art
Image pickup apparatuses these days, such as video cameras, digital still cameras, and broadcast cameras, which use solid-state image pickup elements, and silver-halide film cameras, have high performance and compact bodies. There are demands for short, compact, high-resolution zoom lenses that serve as imaging optical systems used with these image pickup apparatuses.
In addition, the zoom lenses are expected to have wide field angles and high zoom ratios.
An example of the zoom lens that meets the above-described demands is a four-unit zoom lens, which has four lens units, namely, in order from the object side to the image side, a first lens unit having positive refractive power, a second lens unit having negative refractive power, a third lens unit having positive refractive power, and a fourth lens unit having positive refractive power.
U.S. Pat. No. 7,193,790, and Japanese Patent Laid-Open No. 2006-113453 disclose rear-focusing four-unit zoom lenses that perform zooming by moving the first, second, and third lens units and correct image plane variation caused by zooming by moving the fourth lens unit.
United States Patent Application Publication No. 2007/0091460 discloses a rear-focusing four-unit zoom lens that vibrates the entire third lens unit in a direction perpendicular to the optical axis to form a still image.
In general, the size of a zoom lens can be reduced by increasing the refractive power of the lens units constituting the zoom lens and reducing the number of lenses.
However, in such a zoom lens, as the refractive power of the surfaces is increased, the thickness of the lenses is also increased. This makes it difficult to sufficiently reduce the length of the zoom lens or correct aberrations.
To obtain high zoom ratio and compact rear-focusing four-unit zoom lenses having high optical performance, it is important to appropriately set the refractive power, configuration, and the like of the lens units.
In particular, unless the refractive power of the third and fourth lens units as well as the configuration of the third lens unit are appropriately set, it is very difficult to produce rear-focusing four-unit zoom lenses having high zoom ratio and high optical performance over the entire zoom range.